The invention relates to a process for preparing ethylenediamine by hydrogenation of aminoacetonitrile over a catalyst.
Ethylenediamine (EDA) can be prepared by hydrogenation of aminoacetonitrile (AAN) and is a starting material for, for example, the synthesis of complexing agents or bleaching activators which are used, inter alia, as additives for laundry detergents or cleaners.
It is generally known that nitriles can be hydrogenated in the presence of catalysts to give the corresponding amines. Depending on the reaction parameters selected, the known processes give the desired products, for example primary amines as main product and secondary and tertiary amines as by-products. A problem here is often that the desired product is obtained with lower selectivity and/or in lower yield, frequently also accompanied by rapid deactivation of the catalyst used.
Numerous processes for hydrogenating the α-amino nitriles aminoacetonitrile (AAN) and iminodiacetonitrile (IDAN) or β-amino nitriles have been described in the prior art. Thus, it is known that the hydrogenation of β-amino nitriles generally proceeds without problems, while the hydrogenation of α-amino nitriles is associated with the occurrence of numerous disadvantages such as hydrogenolysis of the C—CN bond or the R2N—C bond, “Handbook of Heterogeneous Catalytic Hydrogenation for Organic Synthesis, pp. 213 to 215” indicates the problems of the hydrogenation of α-amino nitriles for the example of α-alkylamino nitriles or cyclic α-aminonitriles compared to β-amino nitriles. The known stability problems of α-amino nitriles are presumably the reason why to the present day only the hydrogenation of the α-amino nitriles AAN or IDAN to EDA (ethylenediamine) or DETA (diethylenetriamine), respectively, has been described in detail. However, a corresponding hydrogenation is not known for higher α-amino nitriles.
The stability of AAN also differs significantly from the stability of IDAN, as can be shown by dynamic differential calorimetry. While the onset is at 220° C. in the case of IDAN, in the case of AAN decomposition is observed at a temperature as low as 150° C.
In processes for preparing amines by hydrogenation of nitriles, it is also known that a certain amount of ammonia favors the selectivity of the hydrogenation to primary amines and suppresses the formation of secondary and tertiary amines. However, the hydrogenation in the presence of ammonia involves an additional engineering outlay associated with separation from the product stream, work-up and possible recirculation of the ammonia. In addition, relatively high pressures can be necessary in the hydrogenation, since the partial pressure of the ammonia has to be taken into account.
DE-A 3 003 729 describes a process for hydrogenating aliphatic nitriles, alkylene oxy nitriles and alkylene amino nitriles to primary amines over a cobalt or ruthenium catalyst in the presence of a solvent system. The solvent system used comprises water and ammonia together with an ether or polyether which preferably has from 4 to 6 carbon atoms and a hydrocarbon to oxygen ratio of from 2:1 to 5:1, e.g. dioxane, tetrahydrofuran, methylene glycol dimethyl ether or diethylene glycol dimethyl ether, with cyclic ethers such as dioxane and tetrahydrofuran being particularly preferred. As nitrile component, dinitriles are particularly preferred. On the other hand, DE-A 3003 729 does not disclose that compounds which have both a cyano group and an amino group, e.g. such as AAN, can be used in this process.
EP-A 0 382 508 describes a process for the batchwise preparation of acyclic, aliphatic polyamines by hydrogenation of acyclic, aliphatic polynitriles in the liquid phase over Raney cobalt catalysts, for example in the presence of anhydrous ammonia. Here, a polynitrile solution is fed into a reaction zone which comprises the Raney cobalt catalyst in an essentially oxygen-free atmosphere. During the entire time of the reaction, the polynitrile solution is fed in at a rate which is no greater than the maximum rate at which the polynitrile reacts with the hydrogen in the reaction zone. Furthermore, mention is made of a reaction parameter K which is suitable for determining the volumetric feed rate. The process described is restricted to the preparation of polyamines from polynitriles such as iminodiacetonitrile (IDAN), nitrilotriacetonitrile or compounds having more than 2 cyano groups. However, the reaction of compounds having one cyano groups, e.g. AAN to EDA, is not described.
U.S. Pat. No. 3,972,940 relates to a method of preventing foaming of the suspension of a Raney nickel or Raney cobalt catalyst used in the catalytic hydrogenation of nitriles to the corresponding amines. In this method, both the appropriate nitrile and the catalyst suspension are fed continuously into the reaction zone. In the reaction zone, the nitrile used is hydrogenated to the corresponding amine and unreacted nitrile, the catalyst and the amine, in particular hexamethylenediamine, are removed from the reaction zone. Foaming of the catalyst suspension is suppressed by a partial amount of the amine (product) discharged from the reaction zone being introduced into the catalyst suspension before the catalyst suspension is fed into the reaction zone. However, U.S. Pat. No. 3,972,940 gives no information about the rate or amount at which/in which the nitrile used is fed into the reaction zone. Furthermore, neither AAN nor EDA are explicitly mentioned in this document.
U.S. Pat. No. 2,519,803 describes a process for preparing ethylenediamine by hydrogenation of a partially purified aqueous reaction mixture which results from amination of formaldehyde cyanohydrin and comprises aminoacetonitrile as intermediate. The partially purified aqueous reaction mixture is cooled to about 5° C. for a maximum of 30 minutes before it is passed to the hydrogenation. The hydrogenation preferably takes place in the presence of NH3.
DE-A 1 154 121 relates to a further process for preparing ethylenediamine, in which the starting materials hydrocyanic acid, formaldehyde, ammonia and hydrogen are reacted in the presence of a catalyst in a one-pot process. Both the ammonia and the hydrogen are used in a molar excess over the further starting materials hydrocyanic acid and formaldehyde which are present in equimolar amounts. In this process, the AAN formed in situ is thus not isolated but directly reacted further with hydrogen. A disadvantage of this process is that the desired product (EDA) is obtained relatively unselectively in small amounts.
U.S. Pat. No. 3,255,248 describes a process for the hydrogenation of organic nitrogen-carbon compounds which preferably have amino groups substituted by nitro, N-nitroso, isointroso, cyano or aromatics to the corresponding amines in the liquid phase using a sintered catalyst comprising cobalt or nickel. Here, the starting material is trickled, either alone or in the presence of a solvent such as water, tetrahydrofuran, methanol, ammonia or the reaction product formed, together with the hydrogen onto the catalyst. If unsaturated compounds such as cyano groups are hydrogenated on the nitrogen atom, the presence of ammonia in the reaction is recommended. This is made clear in example 1 of this patent, where aminoacetonitrile in the form of an aqueous solution is trickled down with liquid ammonia but without the solvent onto the sintered catalyst. However, U.S. Pat. No. 3,255,248 gives no information about the rate at which the starting material is fed in.
EP-A 1 209 146 relates to a further process for the continuous hydrogenation of nitriles to primary amines, in which the respective nitriles are reacted in the liquid phase over a suspended, activated Raney catalyst based on an aluminum alloy and the reaction is carried out in the absence of ammonia and basic alkali metal or alkaline earth metal compounds. Among many other nitriles, AAN and IDAN can be reacted to give the corresponding ethylene amines. If appropriate, the nitrile to be hydrogenated can also be present in dissolved form in an organic solvent, with preference being given to using alcohols, amines, amides, in particular N-methylpyrrolidone (NMP) and dimethylformamide (DMF) and also ethers or esters as solvents. However, EP-A 1 209 146 gives no information about the rate at which the respective nitrile is fed into the reaction vessel (reactor).